Light emitting elements with point shaped light emission, in particular solid state light emitting elements (e.g. LEDs), are being used more frequently in various lighting devices, including light fixtures for various entertainment lighting applications such as Theatre, TV Studio lighting and illumination at events like e.g. rock concerts.
Solid state light emitting elements have large advantages over conventional lamps in terms of energy efficiency and weight. Especially in temporary applications, such as lighting fixtures used during tours and events, the reduction of total weight is a key benefit of solid state lighting systems.
There are many LED systems on the market with red, green and blue LEDs, where each LED has an individual lens to form a narrow beam. Because in these systems the light is not sufficiently mixed, objects create multiple shadows. In addition, with this system architecture it is not possible to create a hard-edge spot, as is frequently used in entertainment.
It has been shown that a lighting system without these limitations can be created based on an array of 100-200 LEDs, connected to one optical system. This optical system is important to transform the Lambertian light distribution from the LEDs into the required beam shape (10°-40° FWHM, preferably zoomable, well defined beam profile). Such a system is disclosed in U.S. Pat. No. 6,200,002.
The optical system to transform the Lambertian light distribution of the LEDs into a beam usable e.g. in entertainment applications typically comprises a tubular reflector having an entrance aperture and an exit aperture being larger than the entrance aperture and a ratio between the exit aperture diameter and entrance aperture diameter in the range of 6 to 10. Since the total diameter of the system should not become larger than a few tens of cm, the light emitting elements must be confined to an area having a diameter in the order of a few cm.
The output flux of a LED array with a diameter of a few cm is limited by the heat transfer to the environment. In addition, the amount of LEDs is also limited by the package size of the existing efficient LEDs. In order to reach e.g. 10.000 lumen at the current LED efficacy of around 60 lm/W, around 150 W needs to be removed from a few cm2. If this is to be done by a metal heat sink, the weight of the fixture will become large.